Clean up Dockerfile steps

Re-organize, add explanatory comments,
and delete unnecessary package installations.

Dockerfile

@@ -1,30 +1,32 @@
 FROM ruby:2.3.7
 ENV PHANTOM_JS=2.1.1
 
-# Add the apt repository for yarn
-RUN curl -sS http://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
-  echo "deb http://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
+# Add the apt-repository for the latest node.js and install node.js
+RUN curl -sL https://deb.nodesource.com/setup_8.x | bash - && \
+  apt-get install -y nodejs
 
-# Add the apt-repository for the latest node.js
-RUN curl -sL https://deb.nodesource.com/setup_8.x | bash -
+# Add the apt repository for yarn and install yarn
+RUN curl -sS http://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
+  echo "deb http://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && \
+  apt-get update && apt-get install -y yarn
 
-RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
-RUN apt-get install build-essential chrpath libssl-dev libxft-dev -y && \
-  apt-get install libfreetype6 libfreetype6-dev -y && \
-  apt-get install libfontconfig1 libfontconfig1-dev -y && \
-  cd ~ && \
+# Install PhantomJS
+RUN cd ~ && \
   export PHANTOM_JS="phantomjs-2.1.1-linux-x86_64" && \
   wget https://github.com/Medium/phantomjs/releases/download/v2.1.1/$PHANTOM_JS.tar.bz2 && \
   tar xvjf $PHANTOM_JS.tar.bz2 && \
   mv $PHANTOM_JS /usr/local/share && \
-  ln -sf /usr/local/share/$PHANTOM_JS/bin/phantomjs /usr/local/bin && \
-  apt-get install -y yarn
+  ln -sf /usr/local/share/$PHANTOM_JS/bin/phantomjs /usr/local/bin
+
+# Establish working directory in Docker container's /refugerestrooms folder
 RUN mkdir /refugerestrooms
 WORKDIR /refugerestrooms
 
+# Install Gems
 COPY Gemfile /refugerestrooms/Gemfile
 COPY Gemfile.lock /refugerestrooms/Gemfile.lock
 RUN bundle install
 
+# Install Node.js packages
 COPY package.json yarn.lock /refugerestrooms/
 RUN yarn --pure-lockfile